Light valve



1932- D. G. SHEARER ET AL 1,843,989

LIGHT VALVE Filed March 15, 1930 2 Sheets-Sheet l Jwwntow Feb. 9, 1932. D. a. SHEARER ET AL LIGHT VALVE Filed March 15, 1950 2 Sheets-Sheet 2 0M0. m awed Patented Feb. 9, 1932 UNITED STATES A PATENT OFFICE DOUGLAS G. SHEABEB, LOS ANGELES, AND OLINDO O. CECGARINI, OF BEVERLY HILLS, CALIFORNIA, ASSIGNORS TO METRO-GOLDWYN-MAYER CORPORATION, OF CULVER CITY, CALIFORNIA, A CORPORATION OF NEW YORK LIGHT VALVE Application filed March 15, 1930. Serial No. 436,050.

This invention relates to an im roved light valve adapted for use in modu ating light for the recording of voice currents, particularly for reproduction purposes.

The normal light valves of the prior art generally comprise a minute metallic ribbon or tape suspended in aiplane at right angles to a magnetic field. Normally, such ribbons or tapes are carried by an armature plate provided with apole piece and a longitudinal slot in the pole piece, the ribbons lying above the pole piece in the magnetic field, said ribbons vibrating in a plane at right angles to the longitudinal axis of the slit so as to increase or decrease the width of the slot. In

- this manner, a variable density record is proribbons.

It has been found that records produced by light valves of the character described hereinabove and used extensively in the prior art do notrepresent a true record of the frequencies which it is desired to record. The continuous film on which the record is made is moving at a constant speed, and as a result a certain amount of distortion is produced.

An object of this invention is to disclose and provide a device for modulating light so as to obviate the distortion normally encougtered when the valves of the prior art are use Another object is to disclose and provide a device whereby the amplitude of vibrations of the light modulating element may be amlified. p Another object is to disclose and provide a light modulating device capable of producing variable area records of greater clarity and effective range than the light modulating devices of the prior art.

These and other objects, uses and advantages of this invention will become apparent to those skilled in the art from the following detailed description of one preferred form of apparatus disclosed in the appended drawings, in which:

Fig. l is a diagrammatic representation of an apparatus which may be employed in the recordation of sounds.

Fig. 2 is a diagrammatic representation of an oscillatory voice current.

Fig. 3 is a diagrammatic representation of a sound record of the variable density type produced by employing vibrating ribbons whose edges are parallel to the longitudinal edges of the slot through which the light passes.

Fig. 4 is a diagrammatic representation of the distorted sine wave character of the record shown in Fig. 3.

Fig. 5 is a diagrammatic repi'esentation'of a variable area type of record produced in accordance with this invention.

Fig. 6 is a diagrammatic representation of a modified type of record which may be produced by the device embraced by this invention.

Fig. 7 is an enlarged plan view showing the position of vibrating elements with relation to the slot in normal light valves.

Fig. 8 is an enlarged, partly diagrammatic representation of the relation of vibrating light modulating elements with. respect to a light slot in the device embraced by this invention.

Fig. 9 is a transverse section through the device shown in Fig. 8, the section being taken along the plane 99 in Fig. 8.

Fig. 10 is a detailed plan view of one form of device embraced by this invention.

Fig. 11 is a side elevation, partly in section, of the device shown in Fig. 10.

As shown in the drawings, the equipment ordinarily employed in sound recording generally comprises a plurality of micro hones 1, which are connected to a mixer 2 w ich controls the gain of the amplifiers for the recording machine, and permits the mixer operator to combine the contributions of the several microphones. The current then passes through an amplifier 3, one or more equalizers 4, an attenuator 5, and then into the recording machine, generally indicated at 6.

The recording machines include a constant source of light 7, a light valve 8, through which the signal currents from the amplifiers 3 are passed, and a lens system 9 adapted to focus the image of the light valve ribbons on a continuous film 1O fed continuously by suitable mechanism, not shown. Ordinarily, a

condensing lens system 11 is positioned be tween the lightsource 7'and the valve 8 so as to pass a concentrated beam of light through the aperture formed in the armature of t e electromagnet which constitutes a part of the light valve 8.

The light valve 8 normally comprises an armature plate, a pole piece provided with an aperture such as the aperture 12 (Fig. 7), and a loop of metallic tape having parallel portions 13 and 13'. The metallic tape is thus suspended in a plane at right angles to the magnetic field. The spacing between the loop portions 13 and 13 is extremely minute and much smaller than the width of the fixed slot 12 in the pole piece. The portions 13 and 13 of the loop vibrate in the direction of the arrows, shown in Fig. 7, thus increasing or decreasing the width of the eifective opening through which light may pass. If, for example, the signal or voice current of the character shown in Fig. 2 is passed through the apparatus diagrammatically illustrated in Fig. 7, a variable density type of record,

shown in Fig. 3, is produced.

This type of record has certain disadvantages; the major disadvantage is that the record is not a true reproduction of the original.

Distortion is caused by the fact that the film 10 on which the record is recorded moves constantly in a direction coincidental with the movement of one of the ribbons when they are moving toward each other, and in a direction opposed to the movement of the same ribbon when it moves in a way opposite to the other. As a result, the peaks of the curve, such as for example, the peaks 14, 15 and 16 are displaced relatively to each other. The spacing between the peaks 14 and 16, for example, remains substantially the same, but the peak 15 instead of assuming a position intermediate the peaks 14 and 16 is slightly advanced toward one of said peaks. This is noticeable in the variabledensity record 3 by the fact that the gradation of light is not uniform, that is, the peak line 16 does not show an equal grading oif on both sides thereof, but instead shows a more rapid decline on the upper side, namely, the side corresponding to the node 15. During reproduction, therefore, a record of the character shown in Fig. 3 will not be a perfect record and the distortion there exhibited gives rise to harmonics and over-tones which did not exist in the original.

The travel of the ribbons 13 and 13 is extremely minute and rarely exceeds 1 mil. An object of this invention is to provide an apparatus which will be capable of amplifying the effective movement of the light modulating elements, namely, the metallic ribbons or ribbon portions 13 and 13. 7

Furthermore, by so amplifying the effective travel of the ribbons, it is possible to produce a variable density type of record which is not subject to the disadvantages of a record such as that illustrated in Fig. 3.

As diagrammatically shown in .Fig. 8, the invention comprises placing the light modulating elements, such as for example, the ribbon portions 17 and 17 in such .position with respect to a longitudinal slot 12 that the edges of the ribbons 17 and 17' are at an angle to the longitudinal axis of the slot 12. It will thus be seen that the edges of the ribbons 17 and 17', during their vibration in the direction of the arrows, will not increase or decrease the width of the slot 12, but instead decrease or increase the length of the slot. The angle that the edges of the ribbons 17 and 17 make with the longitudinal axis of the slot 12 may vary, depending upon the width of record desired and the electrical and physical characteristics of the circuit.

Mechanically, the amplification of the travel of the ribbon portions 17 and 17' is greater when the angle, such as the angle A, is small and such amplification is reduced when the angle becomes greater. It has been found that in actual practice angles of between zero and fifteen degrees are most satisfactory, and for ordinary purposes an angle of about five degrees may be used. However, the light modulating ribbons may be inclined at any angle between zero and ninety degrees.

Inasmuch as the apertures 12 in normal pole pieces are fairly wide, that is, about 8 mils wide and 250 mils long, it is desirable to mask this opening by means of a small masking plate such as the plate 18 carried by the pole piece 19. Furthermore, the use of a masking means 18 permits the movement of the masking means longitudinally of the slot 12 in the pole piece 19, thereby fixing the ends of the operating aperture or slot through which the light is actually passed.

When two ribbons, or when a ribbon in the form of a loop so as to provide parallel portions 17 and 17' is employed, a double envelope type of record, diagrammatically illustrated in Fig. 5, is produced. If, however, only a single ribbon, such as for example, the ribbon 17, is employedand the portions 17 is removed, then a single envelope type of rec.- ord, shown in Fig. 6, may be produced. Both of these types of records are characterized and 11 in greater detail. As shown therein,

the device comprises an armature plate 20 provided with a pole-piece 19, said pole piece being provided with a longitudinal slot indicated at 12.

The pole piece 19 is preferably provided with plane sides 21, which slidably contact with a turret or turntable 22 provided with a stepped or rabbeted circular edge 23. The turntable 22 rests upon the upper surface of the armature plate 20- and is provided with an aperture 24. The edges 21, therefore, contact with the inner edges of aperture 24 and the turntable or turret 22 is thus movable longitudinally while it encircles the pole piece 19.

The armature 20 also preferably carries a bridge support 25 which is rotatably mounted on the turret 22. The bridge support 25 preferably includes bridge members 26 and 27 mounted on each side of the turret, and thus on each side of the pole piece 19. The bridge members 26 and 27 may be provided with upwardly extending spacing flanges 28 adapted to contact with edges of metallic ribbons or loops such as the ribbon portions 29 and 30, thus maintaining them in spaced relation over the pole piece 19. The bridge members 26 and 27 are also preferably provided with supporting bridges proper 31, on which said ribbons or tapes rest.

The bridge members 26 and 27 may be connected to the bridge supporting member 25 in any suitable manner, as for example, by

, means of screws 32, the upwardly extending flanges 28 being retained in position between the bridge members 26 and 27 by means of .suitable screws 33.

The bridge members 26 and 27 may be provided with anchor means for holding and retaining the ends of the metallic ribbon forming the loop portions 29 and 30. Such anchor members may comprise a stud 34 having a well 35 formed radially therein, said stud being retained in the bridge members 26 and 27 by means of suitable screws 36. The stud 34 may be provided with a longitudinal extension 37. The stud 34 preferably carries a collar 38 adapted to be loosely received on the stud 34, the collar 38 being provided with a longitudinal extension 39 and an internally threaded radial aperture 40 opposing said longitudinal extension 39.

A set screw 41 adapted to be threadedly engaged in the aperture 40 of the collar 38 and provided with a small diameter cylindrical protuberance adapted to be received in the well 35 causes the collar 38 to be retained upon the stud 34, the cylindrical extension of the set screw 41 fitting into the well 35 and thereby preventing rotation of the collar upon said stud. The longitudinal extensions 37 and 39 are thus put together and the free ends of the metallic ribbons 29 and 30 may be introduced between such longitudinal extensions and by tightening the screw 41, firmly retained by the holding means.

The loop portion of the metallic ribbon 29 vided with. slots 2.2 paralleling the aperture or slit 12 in the pole piece 19. Locking screws 48 are provided, thereby providing means for adjustablypositioning the turret or turntable 22 longitudinally of the pole piece 19. The bridge supporting member 25 may also be provided with apertures 49 and with locking screws 50, said locking screws being provided with threaded portions of much smaller cross sectional area than the width of the slot 49, but with sufliciently large heads to bridge the slot 49. It is to be understood that the locking screws 50 and 48 are threadedly engaged at their lower portions with the armature plate 20.

The ends of the bridge support 25 may be provided with lugs or bosses 51. Brackets 52 may be connected to the armature plate 20 exteriorly of the movable bridge support 25, said brackets carrying set screws 53, said set screws being adapted to seat upon the lugs or bosses 51.

By loosening thellocking screws 48 and 50, the entire movable bridge support 25 as well as the turret or turntable 22 may be moved longitudinally by adjusting the set screws 53. After the longitudinal position has been thus established, the locking screws 48 may be tightened, thus rendering the turntable or turret 22 immovable. The rotatable bridge support 25 may then be rotated about the turret 22. This can be accomplished by means of the adjusting screws 54 extending into the body"of the armature plate 20 from opposite sides.

The ends of the adjusting screws 54 project into a recess or chamber 55 formed in the armature plate 20 and abut a movable block 56 slidably received in said well or depression 55, said block 56 being movable transversely to the longitudinal axis of the slot 12, for example. Said block 56 may be provided with a longitudinal depression 57 which slidably receives a pin 58 carried by the movable bridge support 25. By adjusting the screws 54, therefore, the movable bridge support 25 may be angularly positioned about the turret 22. During longitudinal adjustment of the turret and rotatable bridge support, as by means of the adjustment screws 53, the ends of the adjusting screws 54- merely slide upon the outer longitudinal-surfaces of the block 55, longitudinal movement of the rotatable bridge support being permitted with respect to the block 56, by reason of the depression 57 formed therein in which the pin 58 carried by the rotatable bridge support 25 is slidably received.

After the rotatable bridge support 25 has been angularly adjusted with respect to the turret 22, it may be locked in such position by tightening the locking screws 50.

It is to be understood that suitable electrical connections are made to the holding means, such as for example, the studs 34 from the binding posts 60, thereby permitting the supply of current to the metallic loop or ribbons 29 and 30 during operation.

As stated hereinabove, the device described herein may be employed whenever it is desired to place the vibrating metallic elements, such as the ribbons 29 and 30, angularly with respect to the longitudinal axis of the slot.

The means for longitudinally moving thebridge support 25 are alternate members, as it is necessary that the light modulating elements act upon a portion of the slot 12 which permits light to pass upon a desired portion of the film. For example, where the sound is being recorded for use in conjunction with an action picture, it is necessary that the sound record be imprinted upon the film at a point closely adjoining the sprocket holes of the film. By longitudinally'adjusting the rotatable bridge support 25, the exact posi tion of the sound record with respect to the film may be controlled.

Although a specific form of device has been described in great detail, it is to be understood that the invention is not limited there to. The invention broadly relates to a device capable of supporting and maintaining a vibratory light modulating element angularly with respect to a fixed slot in an armature. The advantages of so positioning the light modulating element have been described hereinabove. By providing a device of great flexibility so that the angular position of the vibratory elements can be readily changed, the specific angular position required for a particular set-up of equipment may be readily obtained.

We claim:

1. In a light valve, the combination of an armature plate, a pole piece in said plate, and a bridge rotatably mounted on said armature plate, means for angularly positioning said bridge with respect to said pole piece, and means for longitudinally moving and positioning said bridge with respect to said pole piece.

2. In a device for modulating light, the combination of an armature plate provided with a pole piece, a longitudinal slot in said pole piece, a bridge support rotatably mounted on said armature plate, means for angularly positioning said support with respect to the longitudinal axis of said slot, means for moving said support in a direction substantially parallel to the longitudinal axis of said slot, and means for adjustably positioning said bridge support on said armature, plate.

3. In a device for modulating light, the combination of an armature plate provided with a pole piece, a longitudinal slot in said pole piece, a bridge support rotatably mounted on said armature plate, bridge members carried by said support, a metallic ribbon in loop form carried by said bridge support, a portion of said ribbon being supported in parallel spaced relation by said bridge members, means for angularly positioning said bridge support and metallic ribbon with respect to the longitudinal axis of said slot, means for movin said support and ribbon in' a direction su stantially parallel to the longitudinal axis of said slot, and means for adjustably positioning said bridge support on said armature plate.

4. In a device for modulating light, the combination of an armature plate provided with a pole piece, a longitudinal slot in said pole piece, a bridge support rotatably mounted on said armature plate, bridge members carried by said support, a. metallic ribbon in loop form carried by said bridge support, a portion of said ribbon between said bridge members being in substantially parallel spaced relation above said pole pieces, means for holding the free ends of said ribbon carried by said bridge support means for maintaining said ribbon loop under tension, said means being carried by said movable bridge support, means for angularly positioning said support with respect to the longitudinal axis of said slot, means for moving said support in a direction substantially parallel to the longitudinal axis of said slot, and means for adjustably positioningsaid bridge support on said armature plate.

5. In a device for modulating light, the combination of an armature plate provided with a pole piece, a longitudinal slot in said pole piece, a thin mask carried by said pole piece over said slot, said mask having a slit therein of smaller dimensions than the slot in said pole piece, and a metallic ribbon carried by said armature plate over said slot and mask, the longitudinal axis of said ribbon being at an angle between zero and ninety degrees to the longitudinal axis of said slot and pole piece, means for angularly positioning said support and ribbon loop with respect to the longitudinal axis of said slot and slit, means for moving said support in a direction substantially parallel to the longitudinal axis of said slot and slit, and means for adjustably positioning said bridge support on said armature plate.

7. In a li ht valve, the combination of a movable bri ge support, bridge members car-' ried by said support, an aperture in said bridge support between said bridge members, a metallic ribbon in loop form carried by said bridge support, means for holding the free ends of said ribbon carried by said bridge support, said means comprising a stud, a,

collar provided with a longitudinal extension carried by said stud, means for preventing rotation of said collar on said stud, and means for bringing said longitudinal extension carried by said collar and said stud in contact; and means for maintaining said ribbon loop under tension carried by said movable bridge support.

8. In a device for modulating light, the combination of an armature plate, a pole piece carried by the plate, and a longitudinal slot in said pole piece, a turntable carried by said armature and movable around said pole piece, means for longitudinally positioning said turntable with respect to said pole piece, and a bridge support carried by said armature and rotatable around said turntable.

9. In a light valve, the combination of an armature plate, a pole piece in said plate, a longitudinal slot in said pole piece, a bridge member on either side of said pole piece, said bridge member being adapted to carry a light modulating ribbon, the longitudinal axis of said ribbon lying at an angle of between zero and fifteen degrees to the longitudinal axis of said slot.

10. In a light valve, the combination of an armature plate, a pole piece in said plate, a

longitudinal slot in said pole piece, bridge members on each side of said pole piece, said bridge members being at an angle to the longitudinal axis of said slot and adapted to carrv and support an elastic vibrating ribbon whose longitudinal axis is inclined at an angle of between zero and fifteen degrees to the longitudinal axis of said slot, said ribbon lying above said slot whereby light passing through said slot may be modulated by said ribbon.

Signed at Culver City, Calif., this 12th day of February, 1930.

DOUGLAS G. SHEARER. OLINDO O. CECCARINI. 

